Pain sensitivity of permanent teeth at various stages of development is of clinical concern. The dentist's perception of a tooth's pain sensitivity may influence his treatment. If differences in sensitivity normally exist at different stages of tooth development the dentist should understand these differences and the factors responsible. The first part of the proposed project will provide new information on innervation levels for human teeth at various stages of development, as well as additional information on sensitivity. The parameters to be determined and correlated are: the number of myelinated and unmyyelinated sensitivity of a tooth as determined by electron microscopy, the threshold sensitivity of a tooth as determined by electrical stimulation, the stage of changes and arrangement of intrapulpal nerve fibers with progressive stages of tooth development and aging will also be described. Stage of tooth development will be determined by the degree of root formation in teeth erupted less than five years and by subject age when teeth have been present more than five years. Clinically healthy (no carious lesions; at least half of the bony support; no abrasion and only normal amounts of attrition) mandibular first premolars from humans will be studied at three stages of development: 20 premolars erupted less than five years at various stages of root development; 15 premolars erupted less than five years at various stages of root development; 15 premolars erupted approximately 10 years; 15 premolars erupted approximately 25 years. Pulpal effects with orthodontic treatment are not reported in any detail. The second part of the project will examine the effect of orthodontic tooth movement on intrapulpal nerve fibers. Using as controls appropriate teeth from the first part of the study, ten premolars will be examined in this part. Numbers of nerve fibers will be determined as well as the percentage which display morphologic changes. Sensitivity tests will be done before tooth movement and prior to extraction. Five teeth will be examined after short periods of movement (less than 10 days) and five at longer periods (1-2 months).